The oil palm (Elaeis guineensis Jacq.) is the main source of vegetable oil in the world and is currently one of the most important crops planted in South East Asia, Africa and South America. The demand for palm oil is high and it has risen steadily for the past decade. As such it is desirable to identify traits that can be exploited to improve palm oil yield. However, the long selection cycle (10-12 years) for oil palm makes traditional breeding programs inefficient at providing improved planting material within a reasonable time frame.
One important trait related to palm oil production is the skin colour of the fruit. The skin color of the fruit of the oil palm can vary considerably based on external appearance, (FIG. 1). By far the most common type of fruit is deep violet to black at the apex and whitish-yellow at the base when unripe. Such a fruit has been described as nigrescens (Hartley, C. In: The Oil Palm. 47-94 (Longman, 1988)). The color of the nigrescens fruit varies to some extent on ripening, to either entirely red, or black over the upper half but red at the base (Hartley, C. In: The Oil Palm. 47-94 (Longman, 1988)). Harvesters of nigrescens oil palm fruit have to rely solely on the presence of loose fruits on the ground, detached from the oil palm bunch, to determine that the bunch containing the fruits is ready for harvest. The collection of loose fruits is labor intensive and can occupy up to 28% of the total harvesting time (Hitam, A. et al. In: Proceedings of the 1999 PORIM International Palm Oil Congress (PIPOC)—Emerging technologies and opportunities in the next millennium, ed. A. Darus, C. K. Weng, and S. S. R. S. Alwee, pp 325-336, Palm Oil Research Institute of Malaysia (PORIM), Bangi, Malaysia.). Indeed, difficulty with loose fruit collection is considered a significant contributor to the decline of oil extraction rates (OER) observed in Malaysian Plantations (Corley and Law, Planter, 77: 507-524 (2001)).
The other major fruit type is known as virescens, which is green before ripening and changes at maturity to light-reddish-orange in colour. Inheritance studies indicate that the virescens trait is controlled by a single gene (monogenic) and dominant (Corley and Tinker. In: The Oil Palm 4th edn, 287-325 (Blackwell Science, 2003))). Generally, fresh fruit bunch (FFB) yields of more than 30 tons/ha, with oil/bunch ranging from 29-30%, have been reported in progeny testing involving virescens palms (Wahid and Rajanaidu. Oil Palm Breeding and Competitive approaches. Agriculture Biotechnology International Conference (ABIC), 12-15 September, 2004. Cologne, Germany.) and the yield profile is similar to nigrescens palms.
Both the nigrescens and virescens fruits occur in wild-type oil palm populations. However, although the virescens trait is dominant, the number of virescens palms found in natural populations is small, perhaps suggesting that they have been selected against by farmers or could have associated negative traits. In Nigeria for example only 50 of 10,000 bunches observed were virescens, while in Angola only 72 of 10,000 bunches observed were virescens, (Hartley, C. In: The Oil Palm. 47-94 (Longman, 1988)). However, as reported by Corley and Tinker (Corley and Tinker. In: The Oil Palm 4th edn, 287-325 (Blackwell Science, 200)3)), Rajanaidu found 6% virescens palms among his collections in Cameroon (Rajanaidu, N. In: ni Proc. Int. Workshop. “Oil palm germplasm and utilization”. Palm Oil Res. Inst. Malaysia. 59-83 (1986)). Currently, commercial plantations primarily utilize nigrescens palms. However, virescens, palms can be more desirable to planters as the clear difference in colour between ripe and unripe bunches make it easier to identify ripe bunches, particularly in tall palms, where bunches can be obscured by fronds.
Traditional methods do not allow identification of the fruit type of a given plant until it has matured enough to produce a first batch of fruit, which typically takes approximately six years after germination. In plantations desirous of introducing viriscens materials, significant land, labor, financial and energy resources are invested during the interval from germination to fruit production, some of which will ultimately be of the nigrescens fruit types. By the time nigrescens palms are identified, it is impractical to remove them from the field and replace them with virescens palms, and thus growers will have a mixture of both types of palm plants, which may affect yields for the 25 to 30 year production life of the plants due to inefficient identification of ripe nigrescens bunches. Similarly, the long selection cycle of 10-12 years from seed to seed makes it laborious to use traditional breeding methods to identify or develop true breeding strains of virescens palm oil.